Insects hear through varying organs

Biological structures that sense sound evolved in different ways to suit animal

November 30, 2012

When I was a kid, we had a neighbor who had a big, loud dinner bell. She'd stand on her porch and ring the bell when she wanted her children to come in for supper.

I still remember sitting on the ground watching some ants marching down the sidewalk when the neighbor lady rang the bell. The ants broke their line and scattered in all directions in apparent panic. They soon regrouped and continued about their business. She rang the bell again and the same thing happened.

If you look at the magnified head of an insect, you will not find any ears, but it is apparent that at least some of them can hear. Many insects make sounds, especially those such as crickets and cicadas that have mating calls, so they certainly must be able to hear them. Even insects that do not make sounds need to hear to avoid approaching dangers.

Article Photos

File photoThe praying mantis is unique because it is the only creature in the animal kingdom with just one ear. The ear is slit with a membrane under it on the underside of the thorax, between the middle pair of legs. Mantises often fly at night and can fall prey to bats, which hunt by sending out bursts of ultrasound that work like radar. The mantis ear can pick up the frequency of bat radar and take evasive action.

Before much was known about ant sounds, ants were thought to be unable to hear airborne sounds. It was assumed that they could only feel vibrations through whatever surface they were standing on, via sensitive hairs on their "knees."

Many species of ants make squeaks to communicate with each other by rubbing body sections together, a process called stridulation. Some species of ants squeak loud enough for a person to hear, if they get close enough. The many uses of ant sounds within colonies were unknown until recent years when better amplifying and recording equipment was invented.

However, once it was learned that they actually communicate by sounds, the question was exactly how they hear. Researchers are still working on this. Since ants seldom react to all of the huge, loud human-made noises in the environment, it is thought that they can hear small sounds at a close range by means of organs on their antennae.

The typical "singing" insects such as crickets, grasshoppers and cicadas, as well as some moths and butterflies, hear with what are called tympanal organs. As the name tells us, these organs are like drums, with a membrane stretched over an air space. Sounds cause the "drum" to vibrate, much like our eardrum. Crickets have tympanal organs on their front legs, grasshoppers on the thorax, cicadas on the abdomen. Tympanal organs are in pairs, like our ears.

The praying mantis is very unusual because it is the only creature in the animal kingdom with only one ear. The ear is slit with a membrane under it on the underside of the thorax, between the middle pair of legs. Mantises often fly at night and can fall prey to bats, which hunt by sending out bursts of ultrasound that work like radar. The mantis ear can pick up the frequency of bat radar and take evasive action. That is (at least so far) the only known function of this ear.

Mosquitoes and fruit flies hear with something called a Johnston's Organ. It is a receptor near the base of the antennae, and it detects vibration.

Some insects, especially some fuzzy or hairy caterpillars, sense sounds through vibration of delicate hair on their bodies. If you make a loud noise close to them, they will sometimes freeze or curl up in a ball or even rear up in a fighting position.

Honey bees sense vibrations on a surface through organs on their legs. They also have hearing organs on their antennae. They hear in the frequencies used to communicate inside the hive, where the younger bees work. When they are old enough to go outside and forage, they develop antenna sensors that detect the frequencies used to communicate about food sources.

- Send your insect questions to Claire Stuart by e-mail at buglady@wv.net or write her (with self-addressed stamped envelope) in care of Living Section, The Journal, 207 W. King Street, Martinsburg, WV 25401.